Propellant composition containing beryllium and an energetic difluoramino containing binder

ABSTRACT

A high energy composite propellant composition comprising a fuel component of beryllium, beryllium hydride and mixtures thereof in an energetic difluoramino containing binder material such as 2,3bis(difluoramino)propyl acrylate (NFPA) addition polymerized with a vinyl monomer such as 2-hydroxyl propyl methacrylate and further plasticized with 1,2,3-tris( Alpha Beta bis(difluoramino)ethoxy) propane (TVOPA), additional oxidizer such as ammonium perchlorate in amount sufficient to assure complete oxidation of the binder and fuel component and cured.

Elnited States Patent [1 1 Randolph et al.

[451 Aug. 20, 1974 PROPELLANT COMPOSITION CONTAINING BERYLLIUM AND AN ENERGETIC DIFLUORAMINO CONTAINING BINDER Inventors: Kendall B. Randolph, Annapolis,

Md.; Lewis B. Childs, Fairfax, Va.

Assignee: The United States of America as represented by the Secretary of the Navy, Washington, DC.

Filed: Apr. 29, 1969 Appl. No.: 823,241

US. Cl l49/19.3, 149/19.4, 149/19.5, 149/19.6, 149/19.91, 149/38, 149/42,

Int. Cl C06b l/04 Field of Search 149/109, 76, 45, 87, 42, 149/46, 43, 92, 61, 19', 85, 20, 44, 38, 75

References Cited UNITED STATES PATENTS 7/1967 Guthrie et a1 149/109 3,351,505 11/1967 Shapiro et a1 149/44 X 3,439,017 4/1969 Stevens 149/44 X 3,441,549 4/1969 Gardiner et a1.... 149/44 X 3,441,550 4/1969 Zimmerman 149/44 X 3,447,323 6/1969 Allan 149/36 X Primary ExaminerStephen .1. Lechert, Jr. Attorney, Agent, or FirmR, S. Sciascia; J. A. Cooke 5 7 ABSTRACT 8 Claims, No Drawings PROPELLANT COMPOSITION CONTAINING BERYLLIUM AND AN ENERGETIC DIFLUORAMINO CONTAINING BINDER BACKGROUND OF THE INVENTION This invention generally relates to novel propellant compositions and more particularly to an energetic composite propellant composition.

The development of high speeds and high thrusts is a major concern in the field of modern rocketry. In order to achieve these desired properties the use of high energy fuels is essential. Among such high energy fuels are included beryllium and beryllium hydride and mixtures thereof because these solid materials offer the ultimate in theoretical performance. Heretofore, however, the mainstream of propellant development to incorporate these high energy fuels has been in the area of the double-base formulations of nitrocellulose and nitroglycerin. Although, these formulations possessed certain advantages, combustion problems therein have resulted in significantly lower than theoretical performance efficiencies. These problems experienced by the prior art beryllium and beryllium hydride containing propellants are caused mainly by the formation of beryllium oxide (BeO) particles during the combustion process. For example, the BeO forms a coating about the desired beryllium particles and thereby inhibits the burning process since it is necessary to expend valuable heat energy in order to first melt the BeO layer before the burning of the desired beryllium fuel will begin.

Furthermore, the presence of undue amounts of solid or liquid BeO particles in the propellant exhaust results in added reductions in the delivered specific impulse efficiencies of these prior art formulations due to the phenomenons of lag-loss and two phase flow effects. The specific impulse efficiency of a propellant composition is the ratio of the actual specific impulse to the theoretical specific impulse.

Since beryllium and especially beryllium hydride are low density materials, the double-base propellants of the prior art incorporating these materials have also been of a low density. Low density propellant compositions are obviously disadvantages since they demand more operational space and thereby larger and heavier rocket motors in order to deliver an equivalent amount of energy as a higher density formulation. Moreover, because of this low density the density specific impulse values (which are a measure of the energy) of these prior art compositions are concomitantly lower than desired.

SUMMARY OF THE INVENTION lt is therefore an object of this invention to provide a new high energy composite propellant composition.

viding a composite solid propellant comprising an oxidizer, a beryllium, or beryllium hydride or mixtures thereof fuel, in an energetic difluoramino polymeric binder matrix.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The composite solid propellants of this invention are prepared by the admixture of a fuel metal of either beryllium, beryllium hydride or mixtures thereof with an energetic difluoramino group containing polymeric binder matrix material and a solid oxidizing agent.

The beryllium, beryllium hydride and mixtures thereof fuel components of the present compositions are high energy materials. Generally, the quantity of fuel used in the compositions is dependent upon which of the fuel materials is employed. When free beryllium metal is utilized anywhere in the range of approximately 6 to 18 percent by weight of the total composition is found to be operable, however, for optimum results, it is advantageous to employ about 12 percent by weight of the total composition. In light of the very low density of beryllium hydride (BeH- the amount which may be used in the composition is generally dependent upon the lowest overall density of the propellant composition which can be tolerated. For the purposes of this invention, it is desirable to employ Bel-I from about 8 to about 25 percent by weight of the total composition, with optimum results being achieved at about a 15 percent by weight content. It is also desirable for the purposes of this invention to utilize mixtures of beryllium metal and beryllium hydride as the fuel component of the present compositions. When this is the case, approximately from about 7 to 17 percent by weight of this fuel mixture is used wherein the ratio of Be to Bel-l may vary from 0 to to 100 to 0 parts by weight, respectively.

The difluoramino group containing polymeric binders of the present invention are also high energy ingredients and yield a high theoretical performance. Besides improving the propellant density of the compositions, these energetic binders provide fluorine for the oxidation of the fuels to the corresponding gaseous fluorides. This formation of gaseous oxidation products, such as beryllium fluoride (BeF during the combustion process in place of some of the liquid and solid oxides, aids in the reduction of efficiency due to lag-losses and two phase-flow effects which are associated with the formation of solids and flow of condensed phases in the rocket or other propelled vehicle motor. In this respect, any energetic difluoramino group containing polymer material may be used as the binder material in the practice of this invention. These difluoramino binder materials are the addition polymerization products of an energetic difluoramino-vinyl containing monomer and another essentially non-energetic vinyl group containing monomer possessing hydroxy, carboxy, epoxide or anhydride functionality. An energetic difluoramino group containing plasticizer is further admixed with this addition polymerized product to complete the binder material. No further treatment of this binder is necessary prior to actual propellant mixing. Specifically, some of the energetic difluoramino containing monomers which are employed in the preparation of the addition polymerized product are 2,3-bis(difluoramino)propyl acrylate (NFPA), poly[1,2- bis(difluoramino) 2,3-epoxy1propane (PBEP), 2,3-bis(difluoramino)propyl methacrylate (NFPMA) and l,2,4,5 tetrakis(difluoramino)amyl methacrylat (TAMA).

Some of the vinyl containing monomers possessing hydroxy, carboxy, epoxide or anhydride functionality which may be used for the purposes of this invention are, for example, 2-hydroxyl propyl methacrylate (HPMA), 2-hydroxyl propyl acrylate (HPA), acrylic acid (AA), methacrylic acid, glycidyl methacrylate, glycidyl acrylate, 2-hydroxylethyl acrylate, 2- hydroxyethyl methacrylate, maleic anhydride and the like. Among the energetic difluoramino containing plasticizers which are operableherein a .l,2,3-tris[a,

B-bis( difluoramino)ethoxy] propane, hexakis(difluoramino) propylether (HPE), l,2-di[2,2,3- tris( difluoramino)propoxy] l ,2-

(lTl percent from about 4,000 to about 28,000. Pref erably the M of the addition products are from about 6,0007,000. The amount of energetic plasticizer which is admixed with the addition polymerization product to complete the binder material of the present invention may vary from about 50 to 80 percent by weight of the total binder material wherein optimum results are achieved in the vicinity of about 67 percent. The binder material comprises from about 35 to about 55 percent by weight of the total composition, preferably about 40 percent.

Subsequent to the admixture of the aforeidentified binder material with the remainder of the propellant ingredients, a cross-linking agent, in amounts of from about 0.5 to 5 percent by weight of the total propellant mixture is added and the mixture is cured. Among the cross-linking agents which are operable herein are any of the di-or trifunctional epoxides and isocyanates or any other materials which are conventionally employed as cross-linking agents for the curing of hydroxy, carboxy and anhydride functional polymers. More specifically, some of these are Unox 221, a difunctional cycloaliphatic epoxide product of the Union Carbide Corporation, (Formula I) Araldite 178 (Formula ll) and 179 (Formula I) which are also difunctional cycloaliphatic epoxide products of the Ciba Corporation, any of the bisphenol A- epichlorohydrin epoxides, tolylene diisocyanate, hexamethylene diisocyanate and the like.

Formula I Formula II A solid organic or inorganic oxidizing agent which is compatible with the other ingredients of the propellant mixture and is capable of reacting with the matrix and fuel ingredients in combustion processes should be used for the purposes of this invention to supplement the energetic binder to assure complete propellant oxidation. Such suitable oxidizing agents include ammonium perchlorate, nitronium perchlorate, hydroxylammonium perchlorate and its derivatives, hydroxylammonium nitrate and its derivatives, potassium perchlorate, ammonium nitrate, and potassium nitrate. Also, suitable organic derivatives of nitrous acid, nitric acid, hydrogen peroxide, chromic acid, and perchloric acid can be employed as oxidizers, as well as RDX, HMX and nitramide. Also, when specific characteristics are required, two or more inorganic or organic oxidizing agents may be mixed together in the propellant composition.

Other additives normally incorporated into composite propellants may be added herein, such as curing catalysts, e.g., ferric acetylacetonate, any of the various accelerators, burning rate catalysts, extenders, reinforcing agents, fillers and stabilizers, such as A1 0 The propellant compositions of this invention are also characterized by additional desirable properties not hereinbefore mentioned such as high burning rates, improved tensile properties, improved easy processing, thermal stability, long storage life. Moreover, the compositions of the present invention do not require stabilizing materials as 2-nitrophenyl amine and ethyl centralite as do prior compositions which deleteriously act to dilute the energetic materials of a propellant composition.

The general nature of this invention having been set forth, the following examples are presented as illustrations thereof. It will be understood that the invention is not limited to these examples but is susceptible to various modifications readily apparent to one of ordinary skill in the art.

(addition product is NFPA/HPMA, EHO, intrinsic viscosity 0.28, M 20,000)

Example 3 Composition 7c weight at a temperature of about 5065C for a complete day or more.

The preparation of the binder material follows the 15.27 BeH 44,73 f um ercn following general sche me, however, other procedures A0 gvgg g gi gz g qqy 2 l 5 known tothose skilled 1n the art may also be employed. 3960 (addmo prod; fifigggf gai The energetic monomer, such as NFPA, is added to- 9 0/l0, intrinsic viscosity 0.28, gether with the other monomer, e.g., HPMA, ancl an M-vzoroool initiator to the polymerization solvent. Polymerization occurs during a 24 hour reflux to produce the addition Example 4 10 product. After polymerization the material is stripped Com 05mm 7 Wei h! of the solvent and the plasticizer is added thereto in so- 2 I 0 n86 Be p g lution. The solvent then stripped by heat and vacuum 47.04 ammonium perchlorate and no further treatment is required until propellant 0.10 Alon c (A1 0,) 1.44 Unox 221 38.56 TVOPA/NFPA addtion product 2/1 I 5 Table 1 below summanzes the densmes, specific 1m- P1 121 Q pulse and specific impulse efficiencies of some of the V15 y propellant compositions of the present invention.

Table l lsp efficiency, percent(measured) lsp at l5" cone lsp (theoretical) angle lb.sec/lb theoretical lsp Composition lbs/cu in. (0 cone angle) at 0 cone angle Example 1 0.0528 299.1 91.7 Example 2 0.0628 287.9 94.0 Example 3 0.0493 304.8 90.0 Example 4 0.0639 287.6 95.3 Example 5 0.0636 287.4 92.7

Example 5 Many modifications of the present invention may be made without de artin from the s irit or sco e 40 P g p p Composition 7: weight e eo Be What is claimed and desired to be secured by Letters 47.14 ammonium perchlorate I L44 Unox 22] Patent of the United States 1s. 38.56 TESZR qit ipg ixpggctgw l. A composite propellant composition comprising:

(a man pro uct1s intrinsic viscosity 034' MY 6600) 45 (l) a fuel component selected from the group consist- Similarly, other compositions are prepared employing any of the other ingredients hereinbefore identified.

The compositions of Examples 1 to 5 and the other propellant compositions of this invention may be prepared by employing the following general scheme, however, other conventional methods may also be used. The binder material and the fuel metal component are premixed under vacuum conditions and at an elevated temperature of about C. The oxidizing agent is added in increments with mixing under vacuum and elevated temperature conditions to this binder-fuel premix. After all of the oxidizing agent is added, the mixture is stirred further for about 2 hours longer. At this point, the cross-linking agent is added and the mix ture is stirred for approximately 5 or 10 minutes under vacuum conditions. This total mixture is then cast and allowed to cure in an oven for about 24 hours or more ing of beryllium, beryllium hydride, and mixtures thereof; (2) an energetic difluoramino group containing polymeric binder component which is comprised of the material resulting from the admixture of an energetic difluoramino group containing plasticizer and the addition polymerization product of an energetic vinyl difluoramino containing monomer with an esentially non-energetic vinyl monomer possessing hydroxy, or carboxy, or epoxide or anhydride functionality and a crosslinking agent, wherein the binder component is present in an amount of from about 35 to 55 weight percent of the total composition; and (3) a solid oxidizing agent component in amount sufficient to provide for complete oxidation of said binder and said fuel component.

2. The propellant composition of claim 1 wherein said solid oxidizing agent component is selected from the group consisting of ammonium perchlorate, nitronium perchlorate, hydroxylammonium perchlorate, hydroxylammonium nitrate, potassium perchlorate, am-

monium nitrate, potassium nitrate, cyclonite and homocyclonite.

3. The propellant composition of claim 1 wherein said fuel component is beryllium.

4. The propellant composition of claim 1 wherein said fuel component is beryllium hydride.

5. The propellant composition of claim 1 wherein said fuel component is a mixture of beryllium and beryllium hydride.

6. The propellant composition of claim 1 wherein said energetic plasticizer is selected from the group consisting of l,2,3-tris[a,B-bis(difluoramino)ethoxy] propane, hexakis (difluoramino) propyl ether, 1,2- di[ 2,2,3-tris (difluoramino) propoxy] -1,2- bis(difluoramino) ethane and 2,3-bis(difluoramino) propyl 2,2-dinitropropyl carbonate said energetic vinyl-difluoramino monomer is selected from the group consisting of 2,3-bis( difluoramino) propy] acrylate, poly[l,2-bis(difluoramino)2,3 epoxy] propane, 2,3-

lected from the group consisting of a difunctional cycloaliphatic diepoxide, and a diisocyanate.

7. The propellant composition of claim 1 wherein said addition polymerization product has a number average molecular weight of from about 4,000 to about 28,000.

8. The propellant composition of claim 7 wherein said number average molecular weight is from about 6,000 to about 7,000. 

2. The propellant composition of claim 1 wherein said solid oxidizing agent component is selected from the group consisting of ammonium perchlorate, nitronium perchlorate, hydroxylammonium perchlorate, hydroxylammonium nitrate, potassium perchlorate, ammonium nitrate, potassium nitrate, cyclonite and homocyclonite.
 3. The propellant composition of claim 1 wherein said fuel component is beryllium.
 4. The propellant composition of claim 1 wherein said fuel component is beryllium hydride.
 5. The propellant composition of claim 1 wherein said fuel component is a mixture of beryllium and beryllium hydride.
 6. The propellant composition of claim 1 wherein said energetic plasticizer is selected from the group consisting of 1,2,3-tris( Alpha , Beta -bis(difluoramino)ethoxy) propane, hexakis (difluoramino) propyl ether, 1,2-di(2,2,3-tris (difluoramino) propoxy) -1,2-bis(difluoramino) ethane and 2,3-bis(difluoramino) propyl 2,2-dinitropropyl carbonate said energetic vinyl-difluoramino monomer is selected from the group consisting of 2, 3-bis(difluoramino) propyl acrylate, poly(1,2-bis(difluoramino)2, 3 epoxy) propane, 2,3-bis(difluoramino propyl methacrylate and 1, 2,4,5 tetrakis (difluoramino) amyl methacrylate and said essentially non-energetic vinyl monomer is selected from the group consisting of 2-hydroxypropyl methacrylate, 2-hydroxypropyl acrylate, acrylic acid, methacrylic acid, glycidyl methacrylate, glycidyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate and maleic anhydride and said cross-linking agent is selected from the group consisting of a difunctional cycloaliphatic diepoxide, and a diisocyanate.
 7. The propellant composition of claim 1 wherein said addition polymerization product has a number average molecular weight of from about 4,000 to about 28,000.
 8. The propellant composition of claim 7 wherein said number average molecular weight is from about 6,000 to about 7,000. 